The invention concerns a support surface for a medical examination table for carrying out X-ray examinations and for carrying out surgical interventions with the intra-operation use of X-ray devices, including a table plate and a guide unit couplable with a support column of the examination table, the guide unit having a first guide housing in which the table plate is guided for movement in its longitudinal direction.
Special examinations and surgical interventions (for example in vascular surgery) require a relative movement between the X-ray device and the investigation field, since the field can extend over a relatively large area, which is larger than the static image field of the X-ray device. An adjustment of the X-ray device is possible only to a limited extent, so that it is necessary to shift the support surface of the examination table with the patient. To make possible an unhindered use of the X-ray device, no disturbing obstructions may be located below the examination field. That means, that the support surface must extend far beyond the support column of the examination table.
Support surfaces of the aforementioned kind for X-ray examinations, for example with heart catheters, are known. In these support surfaces the table plates are however provided with metal rails which are guided in special guide elements of the guide unit for longitudinal movement of the table plate. These guide rails make themselves noticeable as shadows in the X-ray image, behind which no body structure of the patient is any longer recognizable. The area in which these guide rails are located is therefore not ray transmitting in an artifact free manner.
The length of the guide rails is determined by the size of the guide length which is necessary to react the resulting rotary moment produced by the weight of the patient, and by the stroke required for the longitudinal shifting. Accordingly the area of such a support surface which is not free for ray transmission in comparison to the size of the field to be examined is very large. The entire length of the support surface includes the length of the guide rails and the length of the fully ray transmissible xe2x80x9cusable areaxe2x80x9d, so that a large longitudinal extent of the system is obtained.
A support surface of the aforementioned kind is known from U.S. Pat. No. 4,700,938. The support surface described there consists of a foam material core and an outer shell of carbon fiber strengthened plastic. The outer shell consists of an upper portion, a lower portion and two C-profiles, which extend along the longitudinal edges of the table plate and at their C-legs are connected with the upper portion and the lower portion. The table plate lies on rollers which are supported in a support column. Two other track rollers are rotatably supported on the supporting column, each of which extends inwardly into a respective one of the C-profiles and lies on the lower C-leg of the C-profile, which together with the lower portion of the outer shell of the table plate forms a double layered edge strip. The upper C-legs of the C-profiles, together with a section of the upper portion of the outer shell above each tractor roll are drawn outwardly and bent downwardly somewhat so that these sections form a cover for the track rollers.
The present invention has as its object the provision of an at least longitudinally shiftable patient support surface of the above-mentioned kind, which together with having a short construction length has a large area for free transmission of X-rays and makes possible a large shifting movement in the longitudinal direction.
This object is solved in accordance with the invention by the features given in claim 1.
In the case of the support surface of the invention the non-ray transmitting area of the examination table is limited to the area of the guide unit, which is not accessible for the X-ray device, since it is located below the guide unit of the support column of the examination table. On the other hand, beyond the guide housing the table plate has a artifact free ray transmissibility, since it itself carries no metal parts which can influence the X-ray image. The lack of metallic guide rails or other guide elements is especially advantageous, if for optimal depiction of the examined organs the X-ray device is used with various projection mechanisms. The table plate can also transmit rays transmitted from the side or at an incline from below, without shadows of imaged metal parts hiding the body structure of the patient.
Preferably the table plate is made of carbon fiber reinforced plastic, since this material possesses the advantage of good X-ray transmissibility with at the same time high rigidity.
In a preferred embodiment, the table plate has two edge strips running in the longitudinal direction and a middle section substantially thicker in comparison to the edge strips. This middle section can be of trapezoidal form in a cross section perpendicular to its longitudinal direction, with the underside of the middle section being smaller than the upper side, so that the plate in its middle section tapers diminishingly towards its bottom. Because of the high thickness of the middle section the plate has a high load carrying capacity, with the inclinedly directed side surfaces of the table plate seeing to it that the bright to dark transition at the plate edge does not occur very abruptly in the X-ray picture.
Advantageously the guide elements are upper and lower support or guide rollers which simultaneously lie directly on upper and lower guide surfaces, respectively of the table plate. The upper and lower guide surfaces can in this case be formed on the two longitudinal edges of the table plate on the upper side and lower side respectively of the same. For example, the upper and lower guide surfaces can be formed on the previously mentioned edge strips at both sides of the middle section of the table plate.
The upper and lower guide rollers can be combined so as to be parts of a roller block wherein they are supported by a roller carrier, which carrier is pivotably supported on the guide housing for movement about an axis directed perpendicular to the longitudinal direction and parallel to the table plate, with at least two roller blocks being arranged on each longitudinal side of the table plate on the guide housing. By the provision of several rollers and the incorporation of the rollers into the roller blocks, one achieves a uniform distribution of the load on the rollers. The rollers consist preferably of plastic and to reduce the rolling resistance are preferably supported by roller bearings. By the pivotal support of the roller carriers each of the roller blocks in the case of a bending of the table plate can suit itself to the deformation of the edge strips of the table plate, so that a uniform distribution of the forces on all of the rollers is maintained. In a modified embodiment, the upper guide surfaces can be formed on the edge strips of the table plate, while on the under side of the middle section at least one lower guide surface is provided. This offers the possibility of supporting the middle section of the table plate by at least one guide roller engaging the under guide surface and extending over the entire width of the table plate.
The guide unit can have a second guide housing, on which are provided coupling and guide elements for coupling with the support column and for providing a lateral moment of the support surface relative to the support column. By a releasable connection between the guide unit and the support column support surfaces can be exchanged, and thereby special support surfaces for special examinations or operation disciplines can be used on the same pedestal. Additionally to the longitudinal and lateral shifting of the table plate the possibility can also be provided of adjusting the support surface in height and for inclining it in the longitudinal or lateral direction. Customarily the means for doing these adjustments are provided in the support column.
To avoid, in the case of an inclination of the support surface in the longitudinal direction, the appearance of an unintentional shifting of the support surface due to the resulting inclined drive force arising from the patient""s weight, at least one brake unit is advantageously provided in the guide housing, which brake unit has brake elements, and a positioning mechanism for the brake elements, for engagement with surfaces of the table plate, for example with the upper and/or lower guide surface. Preferably brake units are arranged on both sides of the guide to achieve an increased braking effect, to create redundancy, and to avoid a non-uniform introduction of forces. The brake elements can be formed by two brake shoes which operate on the upper and lower sides of the edge strips of the table plate and which are released by an electromagnet. For safety purposes it is advantageous for the brakes to be active in the unenergized condition, that is for the brake shoes be held applied. The brake force in this case is created by a pre-stressed spring. For opening the brake the electromagnet is excited and releases the brake shoes against the spring force, so that a shifting of the support surface in the longitudinal direction can take place. To avoid that in the case of a bending of the support surface arising from the loading of the support surface a contact of the guide surfaces with the brake shoes occurs, the brake elements and the positioning mechanism are advantageously arranged on a brake carrier, which carrier is supported by means of rollers on an upper guide surface of the table plate and is secured against a movement in the longitudinal direction on the upper guide housing. The entire brake unit is therefore floatingly supported on the table plate by means of rollers and only in the longitudinal direction abuts against the frame of the first guide housing.
The shifting of the table plate can be achieved either manually or by motor. Before a shift the brakes must be first be released. This can be accomplished either by a foot switch or by a manually actuatable switch on the support surface. For safety reasons a release of the brakes should only be possible if the support surface is oriented horizontally, in order to avoid that if the support surface is longitudinally or laterally inclined an uncontrolled moment does not take place. In this case a control is therefore provided which in dependence on the angular position of the head of the support column, by means of which height adjustment, inclination in the longitudinal direction and tipping in the lateral direction is realized, enables or disables the actuation of the brake.
For motorized adjustment of the support surface at least one friction drive can be provided in the guide housing, which drive engages one edge strip of the table plate. The friction drive can for example include a drive roller coupled with a motor and two friction rollers, which friction rollers stand in permanent engagement with the drive roller and are in turn biased against a guide surface of the table plate. The motor is preferably an electric motor. With the inventive solution it is avoided that for reversing the rotational direction of the motor in a linear movement of the table plate, elements such as racks, threaded spindles or tension elements have to be used, which have the disadvantage that they for movement reversal have to lie partially in the ray path of the X-ray device in order to create a large stroke. Thereby shadows are created in the image field which make difficult the supervision in regard to the examination of the body structures. Moreover, since the friction rollers are moveably supported and are biased against the drive roll as well as against the guide path, wear can be equalized and deformation of the support surface by its loading can be taken into account.
For achieving a sufficiently large drive force one must increase the frictional value of the drive rollers by the choice of a suitable work material such as for example rubber or polyurethane. Since these materials have no especially large permissible surface pressure, the achievable pressing force and thereby also the friction force is limited by the given roller width. By the widening of the friction rollers the permissible pressing force for the frictional work material can be so far increased that the drive rollers can at the same time take on the function of supporting the gravity force applied by the plate onto the guide unit. The achievable drive force is in this case directly dependent on the loading of the rollers, which has the advantage that even in the case of a large patient weight and a large unloading of the support surface by way of the guide a sufficiently large drive force is created. By the combination of the two functions xe2x80x9cguidexe2x80x9d and xe2x80x9cdrivexe2x80x9d there results also a simple construction of the longitudinal guiding for the support surface. This advantage especially allows the achievement of the above described solution, in which case the lower guide roller extends transversally across the entire width of the table plate, with this guide roller being connected with a drive motor.
In order to realize the desired shifting of the support surface in the lateral direction, the upper or first guide housing is by means of suitable guide elements shiftably arranged relative to the lower or second guide housing or relative to the supporting column. Therefore, for the required lateral shifting of the support surface it is not necessary to achieve ray transmissible guides since the lower guide housing is located in the region of the support column where no accessible possibility for the X-ray device exists. Therefore here known guide elements can be used. Since the support surface can also be laterally inclined or tilted it is advantageous to provide a brake unit for the lateral guides, in order to avoid an unintentional shifting of the table plate.